» Fri Nov 30, 2012 8:51 am
http://www.uesp.net/wiki/Lore:The_Great_War_(book). Read it.
"In 4E 29, the government of Valenwood was overthrown by Thalmor collaborators and a union with Alinor proclaimed. It appears that Thalmor agents had formed close ties to certain Bosmeri factions even before the Oblivion Crisis. The Empire and its Bosmer allies, caught completely off guard, were quickly defeated by the much-better prepared Altmer forces that invaded Valenwood on the heels of the coup. Thus was the Aldmeri Dominion reborn."
They are allies, but forced allies. Valenwood didn't join the Aldmeri Dominion, it was conquered - with help from within. What's more important, Altmer =/= Thalmor. Thalmor are a minority who seized power and by clever manipulation managed to create quite a bit of strife in Tamriel. Their annexation of Elsweyr was very well executed, reminds me of the way priests in ancient Egypt used their knowledge about solar eclipse to earn respect of the people.
Bosmer are a fascinating nation. Earlier in history they were betrayed both by the Empire and by their own Altmeri brethren, so they tend to keep to themselves and usually don't engage in wars with other nations unless they're provoked. That said, as all elves Bosmer would probably be more likely to stand with the Almer than with the human Empire.
However, both withing Summerset Isles and the forests of Valenwood you can find many people who disagree with the Thalmor and condemn them for usurping the power and dragging their homeland into a war. If you listened to Malborn, and you say you did, then you certainly know that all who oppose the Thalmor - be they Imperials, Nords, Bosmer or Altmer - are severely punished. We heard about purges in Valenwood and there's no reason to doubt the reliability of these rumours because it's certain that when the Thalmor's army marched into Valenwood, many Bosmer fought against them and kept opposing them even after the battle was over.
On the other hand, some will see the rebirth of the Aldmeri Dominion as a glorious success. What your character believes - that you have to decide on your own.